Operational experience with X-ray beam position monitors at the Advanced Photon Source

Photoemission-based X-ray beam position monitors (XBPMs) have been employed in each of the bending magnet (BM) as well as insertion device (ID) beamline front-ends in the Advanced Photon Source storage ring. The position data derived from the BM XBPM blades have been achieved at the few-micron RMS level. Insertion device XBPM-based position data have historically been plagued with problems resulting from background stray radiation impinging on the blades. A method that involves introducing chicanes into the lattice at both sides of the ID was proposed and implemented in APS sector 34 in December 1998, resulting in the elimination of most of the unwanted radiation. The effects of the remaining background radiation were further reduced by a background subtraction procedure. New DSP-based data acquisition and control hardware has been installed that allows the smooth integration of XBPM data with the existing storage ring RF-BPM system. XBPM-based orbit feedback, for a fixed ID gap, has resulted in vertical pointing stability of 0.2 μrad RMS over a 24-h time period. Because of these good results, chicanes have been introduced for six more beamlines and several more are planned in the future. Operational experience with these beamlines is presented and progress on methodologies for reducing gap-dependent orbit motions is discussed